Renovascular disease (RVD) is the most common potentially reversible cause of hypertension and renal failure in the US. Anatomic studies such as x-ray angiography are invasive, use nephrotoxic contrast agents, and do not accurately predict response to revascularization. Functional studies, such as angiotensin-converting enzyme (ACE) inhibitor (captopril) radionuclide renography, can predict response to revascularization, but do not provide important anatomic information for treatment planning. The lack of an accurate diagnostic test has also precluded definitive evaluation of optimal treatment strategies for RVD. Magnetic resonance (MR) imaging offers the unique potential to combine anatomic evaluation about RAS with functional information about renal ischemia and dysfunction in a single clinical examination. Broad, long-term objectives: To reduce the morbidity and mortality associated with hypertension and renal failure due to RVD by correctly diagnosing the disease and by determining which patients are likely to benefit from revascularization therapy and which patients should be treated with medication alone. Specific Aims/Methods: (1) To validate ultra-low dose 3D Gd-DTPA MR renography combined with T1 mapping for the measurement of single kidney GFR and other tracer kinetic parameters as compared with conventional nuclear medicine renography using 99mTc-DTPA. Development and testing of a newly developed automated registration and semiautomated segmentation algorithm will also be completed. (2) To evaluate prospectively the accuracy of MRA combined with ACE-inhibitor MR renography, performed in a single exam, for the diagnosis of RVD, using hypertension and creatinine clearance as measures of response, as well as improvements in single kidney function (see Aim 3). A multi-compartmental tracer kinetic model will also be applied to renography results to identify more sensitive predictors of response to therapy. (3) To conduct a longitudinal study using MR renography to measure response to revascularization in terms of improvements in single kidney function as compared to global kidney function or creatinine clearance. At its conclusion, our study has a high likelihood of showing that the combination of MRA and MR renography, by uniquely providing both anatomic and functional information in a single examination, will accurately diagnose RVD and provide a comprehensive tool for measuring outcomes following therapy.